Street sweeping vehicles are often provided with an auxiliary engine in addition to the main chassis engine. The purpose of an auxiliary engine is to provide a dedicated power source to non-driving functions of the street sweeping vehicle. Examples of non-driving functions are broom operation, blower/fan operation, conveyor operation, and dumping of the hopper. In such arrangements, it is sometimes the case that the chassis engine will also be configured to separately provide power to non-driving functions as well. This allows for the auxiliary engine to be designed at a smaller maximum output capacity since less total load is placed on the auxiliary engine. However, this type of configuration can be disadvantageous in that a failure of the chassis engine system can prevent the operation of some or all of the non-driving functions. Additionally, energy normally lost to heat during braking and deceleration of the vehicle is generally not able to be recaptured in these types of systems. Improvements are desired.